Audio and multimedia systems often include audio input ports for connecting external audio sources. These audio input ports may include analog input ports with two-wire signal lines, which may include tip, ring, sleeve (TRS) sockets or 3.5 mini jacks, or digital input ports with three or more signal lines.
Integrated Interchip Sound (IIS) is one example of a digital interface standard for connecting audio devices. IIS requires at least three different signal lines. These signal lines include a bit clock line, a left-right clock line to indicate left or right channel audio data, and a multiplexed data line containing the left and right channel audio data. Additional multiplexed signal data lines and a master clock line may also be included in different implementations, further adding to the number of signal lines used to transmit audio. The master clock line may transmit a master clock signal at a higher frequency than the bit clock signal. The master clock signal may be used by a digital signal processor to process the audio data.
As the number of signal lines used to transmit audio increases, production costs and power consumption both increase. Production costs increase because it becomes more expensive to manufacture circuit boards, connectors, and wires to support additional signal lines. For example, not only is there an added materials cost for including the additional pin outs and signal lines on the circuit board, but there is also increased power consumption cost because each added signal line consumes additional power. This increased power consumption may reduce the battery life of portable audio devices between charges, requiring the portable device to be charged more frequently.
Thus, there is a need for a digital audio transmission interface using a minimal number of signal lines to transmit audio.